How do I place nodes on the same level in DOT?

Question

I want to render several trees simultaneously and place all root nodes and all leaf nodes on the same level.

Here\'s an example of what I\'m trying to do. Root nodes A a

Answer 1

Here's a simple example inspired by @William John Holden's comment -

graph {
  rankdir=LR;
  a -- b -- c;
  d -- e -- f;
  b -- d; {rank = same; b; d;};
}